Primary and metastatic cancer of the liver presents a significant epidemiologic problem with more than 160,000 new cases anticipated in 2003. Resection offers potential cure but is problematic due to the complex anatomy involved as well as the operative morbidity. The system described in this proposal combines techniques of image guided surgery (IGS) and minimally invasive surgery (MIS) to address these problems. IGS displays surgical position on images to enhance knowledge of local anatomy. MIS uses small-caliber instruments to visualize and manipulate tissue while minimizing the surgical exposure. This project develops a tracked minimally invasive ultrasound to identify anatomy and then register that data to pre-operative imaging. The software designed presents the multi-modal data in an interactive, intuitive form to the surgeon. Ultimately, the success of this project may improve care for and expand the population who will benefit from surgical therapy of liver cancer.